Heap-Based Buffer Overflow in Cesanta Mongoose TLS Handler

CVE-2026-5244

What is CVE-2026-5244?

CVE-2026-5244 is a notable vulnerability found within the Cesanta Mongoose framework, specifically in versions up to 7.20. Mongoose is designed to facilitate lightweight web server and networking functionality for various applications, including IoT devices and embedded systems. The vulnerability arises from a heap-based buffer overflow in the TLS 1.3 Handler due to improper manipulation of the pubkey argument within the mg_tls_recv_cert function. This issue can potentially allow attackers to exploit the vulnerability remotely, leading to severe consequences for affected organizations, including system compromise and data integrity issues. The vendor has promptly addressed this vulnerability by releasing an updated version (7.21) that includes a patch to mitigate the risks associated with CVE-2026-5244.

Potential impact of CVE-2026-5244

1. Remote Code Execution: The buffer overflow vulnerability allows an attacker to potentially execute arbitrary code on the server hosting the Mongoose framework. This could lead to unauthorized system access and control, enabling attackers to manipulate or exfiltrate sensitive data.

2. Denial of Service: Successful exploitation of this vulnerability could lead to a denial of service condition, hampering the availability of the application or service powered by Mongoose. This disruption could severely impact business operations and user experience.

3. Data Leakage: Due to the nature of buffer overflows, attackers may gain access to sensitive information stored in memory. This could result in data breaches where confidential customer data, credentials, or proprietary information is exposed, leading to significant reputational and financial damage for organizations.

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